In quantum physics, there are several experimental observations that suggest that certain aspects of reality can be subjective to the observer. These observations challenge the classical notion of an objective, independent reality and highlight the role of measurement and observation in shaping the observed outcomes. Here are a few key experiments that illustrate this idea:
Double-slit experiment: The double-slit experiment is a classic demonstration of wave-particle duality. When particles, such as electrons or photons, are fired at a barrier with two slits, they can exhibit interference patterns, much like waves passing through the slits. This implies that particles have wave-like properties. However, when the particles are observed or measured to determine which slit they pass through, the interference pattern disappears, and the particles behave like individual particles. The act of observation or measurement collapses the wavefunction and influences the outcome.
Quantum entanglement: Quantum entanglement refers to a phenomenon where two or more particles become correlated in such a way that the quantum state of one particle is inseparably linked to the state of another, regardless of the distance between them. When two entangled particles are measured, their properties become correlated instantaneously, even if the measurements are made far apart. This suggests a non-local connection between the particles. The outcomes of measurements on one particle seem to be influenced by measurements on its entangled partner, regardless of the spatial separation. This implies that the measurement outcome can depend on the observer's choice of measurement.
Delayed-choice quantum eraser: In this experiment, which builds upon the double-slit setup, the choice of whether to observe or erase information about which slit a particle passes through can influence the observed interference pattern. Even after the particle has passed through the slits, the experimenter's choice to measure or erase the which-way information can retroactively determine whether an interference pattern or particle-like behavior is observed. This suggests that the measurement choice made in the future can affect the particle's past behavior.
These experiments, among others, challenge the classical view of an objective reality that exists independently of observation. They demonstrate that the act of measurement or observation in quantum physics has a profound influence on the observed outcomes, suggesting a subjective element to the results. However, it is important to note that the interpretation of these experimental results is a subject of ongoing debate and various interpretations exist within the realm of quantum physics.